1. Field of the Invention
The present invention relates to a projection apparatus and correcting method therefor. More particularly, the present invention relates to a projection apparatus, an illumination module and a color-level correcting method therefor.
2. Description of the Related Art
Referring to FIGS. 1A and 1B, a conventional projection apparatus 100 comprises an optical engine 110 and a projection lens 120. The optical engine 110 includes a light source 112, a color wheel 114, a controlling unit 116 and a light valve 118. The light source 112 is suitable for providing a light beam 112a and the color wheel 114 is configured between the light valve 118 and the light source 112. Furthermore, the controlling unit 116 is electrically connected to the color wheel 114 and the light valve 118.
The color wheel 114 has a red filtering region R, a green filtering region G and a blue filtering region B. The controlling unit 116 is suitable for controlling a rotational speed of the color wheel 114. The light beam 112a provided by the light source 112 passes through the red, the green and the blue color-filtering regions R, G, B in turn to produce red light, green light and blue light. In addition, the light valve 118 is driven by the controlling unit 116 to present different states corresponding to the red, green and blue light. Hence, red, green and blue light are converted into red image, green image and blue image respectively. Thereafter, the projection lens 120 projects the red, green and blue image onto a screen and produce a full color image onto the screen.
In the conventional projection apparatus 100, a signal transmitting device 117 is normally disposed on the color wheel 114. Furthermore, a signal sensing device 119 is also installed at a suitable distance away from the signal transmitting device 117 for receiving the signal 117a transmitted from the signal transmitting device 117. The signal transmitting device 117 follows the rotation of the color wheel 114, so that a time interval between two received signals from the signal transmitting device 117 selecting by the signal sensing device is a rotational period of the color wheel 114. Moreover, the signal sensing device 119 and the controlling unit 116 are electrically connected so that a rotational frequency of the color wheel 114 is computed through the controlling unit 116. Therefore, the passing time for the light beam 112a through the red, greens and blue color-filtering regions R, G, B is computed.
However, slight positional error often occurs in a process of attaching the signal transmitting device 117 to the color wheel 114. Thus, the controlling unit 116 can not accurately compute the respective intervals for the passing time of the light beam 112a through the red, green and blue color-filtering regions R, G and B for controlling the light valve 118. As a result, the color of the image projected by the projection apparatus 100 can not have expected color. At present, one solution is to store a color wheel index in the controlling unit 116 so that the any timing discrepancies between the color wheel 114 and the light valve 118 can be compensated by referring to the color wheel index. With suitable compensation, the timing error is reduced and the image projected from the projection apparatus 100 is more in line with the expected image colors.
The conventional projection apparatus 100 normally has only single color wheel index. However, the signals input into the projection apparatus 100 have different resolutions or vertical synchronous scanning frequencies. Furthermore, the rotational speed of the color wheel changes according to the frequency of the input signal. Therefore, using just one single color wheel index, it is still impossible to compute the intervals for the passage of the light beam 112a through the red, green and blue color-filtering regions R, G and B. Ultimately, the conventional projection apparatus 100 leads to some ruggedness in the color level of the projected image from the projection apparatus 100.